The long-term objective of this program is to understand the mechanism(s) of cellular changes fundamental to neoplastic transformation. Nonneoplastic mammalian cells in culture require a specific hormone(s) and growth factor(s) for initiation of DNA synthesis and mitosis, and an oncogene(s) product(s) may subvert normal growth regulatory mechanisms and lead to neoplastic transformation in culture. This paradigm was assessed in a serum-free bioassay with BALB/MK keratinocytes stably infected with retroviruses containing the "cytoplasmic" oncogenes v-H-ras, v-Ki-ras, v- erbB and v-fms (which encode growth factor receptors), v-fgr and v-mos. Viral transformants grew in serum-free medium containing insulin without epidermal growth factor (EGF), and the v-fgr oncogene abrogated both insulin and EGF requirements. Preliminary studies with v-myc, a "nuclear" oncogene, suggest this gene acts downstream from the insulin/IGF-1 and EGF pathways. Finally, a novel keratinocyte growth factor (KGF) was isolated from serum-free medium conditioned by normal human embryonic fibroblasts. The protein was purified and characterized, and its biologic activity assessed by thymidine incorporation and proliferation assays done in defined medium. Like the FGF family and "cytoplasmic" oncogenes, KGF complements the insulin/IGF-1 signal transduction pathway.